1. Field of the Invention
The present invention relates to a piezoelectric vibrator, and more particularly, to a piezoelectric vibrator that can finely drive a device within a small limited space such as a portable electronic device by generating an elliptical motion using a combination of a longitudinal vibration and a flexural vibration.
2. Description of the Related Art
In recent years, an ultrasonic motor using a piezoelectric vibrator is considered as a new motor replacing an electromagnetic motor. Compared with the electromagnetic motor, the ultrasonic motor using the piezoelectric vibrator has an excellent resolution and a reduced noise and generates no magnetic field.
A piezoelectric element generates a strain with respect to an applied electric field or generates a voltage with respect to a stress. A piezoelectric vibrator or a piezoelectric stator using the piezoelectric element is driven at a resonance frequency ranging from several tens of kHz to several hundreds of kHz, and can transfer an amplified strain to a rotor through a stacked structure or a strain expansion structure. Such a piezoelectric element itself can be used as a vibrator, or it can be combined with a structure having a specific shape.
A piezoelectric ultrasonic motor using the piezoelectric element has a traveling wave driving scheme and a standing wave driving scheme. The piezoelectric ultrasonic motor is driven using a principle of superposing two driving waves having a predetermined phase difference.
Conventional piezoelectric ultrasonic motors are disclosed in U.S. Pat. No. 6,720,711, U.S. Patent Publication No. 2004/0189155, and Japanese Laid-open Patent Publication No. 2004-297951.
U.S. Patent Publication No. 2004/0189155 and Japanese Laid-open Patent Publication No. 2004-297951 provide a piezoelectric ultrasonic vibrator for miniaturization. To this end, conductive films for electrically connecting external electrodes of a first external electrode group to external electrodes of a second external electrode group are formed in close contact with the surface of the ultrasonic vibrator.
However, the conductive films must be formed on the surface of the small-sized vibrator having a rectangular parallelopiped shape. Therefore, there is a limitation in miniaturization of the ultrasonic vibrator. In addition, there is a problem in miniaturization because a plurality of side electrodes used for the external electrode are formed.
Due to the size characteristic of the external electrode, it is practically difficult to form the conductive films on the surface of the vibrator so as to electrically connect the external electrodes of the first external electrode group to the external electrodes of the second external electrode group. An electric short degrades the reliability of product and the production yield.
A problem of the related art including U.S. Pat. No. 6,720,711, U.S. Patent Publication No. 2004/0189155, and Japanese Laid-open Patent Publication No. 2004-297951 is to secure a wire connection in a piezoelectric vibrator body. As the size of the vibrator is decreasing, an electric wiring becomes an important issue. When 0.1 μm strain occurs in the piezoelectric vibrator and a vibration frequency is 250 kHz, an acceleration influencing a solder dot is more than about 200,000 mm/s2. Based on this fact, in the case of a small-sized vibrator where a solder dot is not placed at a nodal point (a position that does not move during vibration), the high acceleration weakens a solder strength, causing a serious problem in operation of the piezoelectric vibrator.